I. Field of the Invention
The present invention relates generally to spinal surgery and, more particularly, to a device for spinal fusion comprising a spinal fusion implant of non-bone construction to be introduced into any variety of spinal target sites.
II. Discussion of the Prior Art
Currently there are somewhere between 500,000 and 750,000 lumbar and cervical spinal fusion procedures performed each year in the United States. One of the causes of back pain and disability derives from the rupture or degeneration of one or more intervertebral discs in the spine. Surgical procedures are commonly performed to correct problems with displaced, damaged, or degenerated intervertebral discs due to trauma, disease, or aging. Generally, spinal fusion procedures involve removing some or the all of the diseased or damaged disc, and inserting one or more intervertebral implants into the resulting disc space.
Minimally invasive methods of performing spinal fusion have gained popularity in recent years due to the many benefits of the procedure which include diminished dissection of body tissue and lower blood loss during surgery resulting in reduced surgery time, lower post-operative pain and a quicker recovery for patients. Transforaminal lumbar interbody fusion (TLIF) procedures provide unilateral access to a desired target site. The TLIF technique involves approaching the spine in a similar manner as a posterior approach but more from the left or right of the spine through a midline incision in a patient's back. This procedure requires only one incision in the back of a patient and involves placing a fusion device into the intervertebral disc space. Introducing the intervertebral implant serves to restore the height between adjacent vertebrae (“disc height”), which reduces if not eliminates neural impingement commonly associated with a damaged or diseased disc. Distraction of the disc space with subsequent decompression of nerve roots can be accomplished by rotating a device between the adjacent vertebrae.
Current spinal fusion implants utilize either bone grafts or artificial implants to fill the intervertebral disc space. Artificial implants may be made of metal, plastic composites, ceramics, bone, or any combination thereof. Natural bone grafts have also been developed including autologous and allograft bone. Other bone grafts may include certain man-made substances including binder joining bone chips and composite bone structures.
While generally effective, the use of bone grafts presents several disadvantages. Autologous bone grafts are obtained from bone material surgically removed from the iliac crest of a patient. This method can be detrimental because it may not yield a sufficient quantity of graft material, requires additional surgery, and increases the risk of infection and blood loss. Moreover, the structural integrity at the donor site can be reduced and significant morbidity associated with harvesting the autologous bone graft may occur.
Allograft bone is obtained from cadaveric specimens, machined, and sterilized for implantation. Production of allograft bone implants may be difficult because of the inherent challenges in forecasting the receipt of cadavers. Furthermore, allograft may only provide temporary support as it is difficult to manufacture the allograft with consistent shape and strength given the differing characteristics of cadavers. Graft material usually has a smooth surface which does not provide good friction between the adjacent vertebrae and slippage of the graft may occur which can cause neural and vascular injury as well as collapse of the disc space.
A need remains for fusion implants that preserve the intradiscal space and support the vertebral column until the adjacent vertebrae are fused and still encourage bone ingrowth to achieve a solid fusion. A need also remains for implants which maximize cortical ring contact (both anteriorly and posteriorly), better facilitate self distraction of the vertebrae during insertion, avoid dural impingement and provide a better fit between anterior edge portions of vertebral endplates.
The present invention is directed at overcoming, or at least minimizing, the disadvantages of the prior art.